New to Dating Issues

Started dating a women again after breaking up with her 1.5 years ago for trust issues. Prior to taking her back, I learned about a guy, 20 years younger than her, she referred to as a "Friend with benefits." I asked her about him and she denied having that type of friendship and he is only a friend. 1. During the evening of our second or third date, she received a text from him at 11:30 PM asking her to come over. She again denied anything was going on. 2. She asked me to meet him and I agreed. When I arrived at the restaurant, she was already there with him and another women. Just a friend of theirs. My girlfriend didn't even stand up to say hello to me and when I leaned in the kiss her hello like I normally do she gave me her cheek. This really hurt.... 3. She invited me to a concert to meet some of her other friends and it was fun. Until she began disappearing with her phone and checking for texts. Shortly there after, this "Friend with benefits" arrived and joined us. She would then excuse herself with him and left. Later, when the concert was over, she could not be found inside or outside the club. Did not answer her phone or text from me or her other friends that also attended the concert with us. I had to call a cab to get home because she was my ride. Prior to my cab arriving she returned and argued for the next day... no intelligible excuses for any of this behavior. I really think I still have issues...any thoughts?